This invention relates in general to the treatment of coke and in particular to a method of treating coke oven gases to recover sulfur from the hydrogen sulfide contained in the gases.
There are known methods providing concentrating the ammonia washed out of a coke oven gas in the so-called deacidizer vapors of a closed-circuit ammonia-hydrogen sulfide scrubber, burning the total amount of the deacidizer vapors, recuperating the heat of combustion in the form of high-pressure steam, removing the condensate, and recovering sulfur or sulfuric acid from the combustion gases. In these methods, the amount of combustion air to be admixed depends on whether the recovery of sulfur or sulfuric acid is sought (German Pat. Nos. 11 63 786; and 12 12 052).
These are non-catalytic methods of burning ammonia and their application in practice has shown that the function and operation of a plant of this kind becomes strongly disturbed if even small amounts of ammonia remain unburned or if other accompanying substances in the vapors, such as hydrocarbons, particularly aromatics, and hydrogen cycanide, do not burn down completely. This results in cloggings, particularly in the piping and the coolers, with the necessity of immediate cleaning of the plant, entailing costly manual labor. The economy of the plant operation is thereby unfavorably affected, since this always requires a shutdown.
Further known is a method of recovering sulfur from the hydrogen sulfide contained in coke oven gases, by partly combusting the hydrogen sulfide to sulfur dioxide and processing the gases in a Claus process to obtain sulfur while simultaneously burning the ammonia carried along, providing washing out of the ammonia and the hydrogen sulfide from the coke oven gas in a closed-circuit ammonia and hydrogen sulfide scrubber. Splitting the deacidizer vapors into substantially hydrogen sulfide free ammonia vapors and substantially ammonia-free hydrogen sulfide vapors, and combusting the ammonia and the hydrogen sulfide vapors each separately while adding firing or combustible gases if needed, wherein the ammonia combustion gases escaping from the waste heat boiler upon being cooled and freed from the aqueous condensate, are added to the partly combusted hydrogen sulfide vapors before their introduction into the Claus furnace (German Pat. No. 19 25 839).
In this method again, the above mentioned troubles have occurred, even though this is a catalytic process of ammonia decomposition and the cause of the troubles may rather be a strongly varying content in ammonia, hydrogen sulfide, hydrogen cyanide, and hydrocarbons of the initial vapors. Then, the addition of air amounts just adequate at the respective instant is difficult to control and it may be necessary to readjust it very soon, if the composition of the vapors changes. If a Claus plant is to operate with an optimum throughput, just one third of the hydrogen sulfide present in the gases to be processed must be oxidized to sulfur dioxide. Under any other oxidation conditions, allowances for losses in the sulfur recovery must be made, even with a formation of salts. This again raises difficulties and inconveniences in the combustion part of the plant, as well as in the Claus plant, wherefrom the waste gases then may fail to have an optimum content in noxious substances, particularly sulfur dioxide. Difficulties arise even in instances where prior to processing them, the vapors are split into hydrogen sulfide vapors with a low ammonia content, and ammonia vapors with a low hydrogen sulfide content, and this is due to the fact that with an irregular load, the splitting column cannot separate the gas stream exactly, so that from undecomposed ammonia and sulfur dioxide in the gas stream, solid ammonium sulfide forms and deposits in the piping and the apparatus. Such a risk is particularly high in this prior art method since after being cooled and separated from the aqueous condensate and prior to being introduced into the Claus furnace, the ammonia combustion gases are united with the partly burned hydrogen sulfide vapors.